I am running LR 5.7 on Windows 10. I have not moved any files, but suddenly, many of my star ratings have gone missing. I have been working in many different folders, and not very systematically, so I am not sure when this happened. It seems that the star ratings that are left are some of the oldest ones in the relevant folders, meaning that I have lost most (perhaps all?) star ratings given during the last months. This amounts to a lot of work in sorting a lot of pictures, so I'm hoping for a fix to restore my lost star ratings.
One thought is that you have opened the wrong catalog file. If you go to File->Open Recent and select each catalog shown there, do you find one with the desired star ratings?
Do you have recent backups of your catalog file that you can check?
Unfortunately, I have the correct file.